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• C~ 1.0 Hydrobgic Mnrtiroring Acrivinu The MB-1 and MB-2R discharges were [ested for pH, total suspended solids, total dissolved solids, and total iron. Results of the analyses aze shown on Table 1.5-1. 1.8 RUNOFF FROM DISTURBED AREAS Flowmeters are installed on discharge points from sediment ponds which dischazge in[er- mittently [o continuously record flows. Information on flows, sampling points, and quality of water discharged from the mine site sediment ponds during WY 1994 is included in Appendix J. Overland runoff from snowmelt and precipitation within the disturbed azeas was routed to one of five sediment ponds on the mine site in WY 1994. The five sediment ponds are designed to contain the predicted runoff from a statistically determined 10- yeaz, 24-hour precipitation event, as well as a calculated sediment storage volume. The three lazger ponds (MB-1, MB-2R and MB3) have additional volume for Mountain Coal Company's storage water rights. The ponds are also designed to pass the overflow from a 25-year, 24-hour precipitation event safely. The West Elk Mine site receives much of its annual precipitation from snowfall during the winter months. When warmer weather begins in late February, March or April, most runoff to the sediment ponds is from snowmelt. It is entirely possible for a volume of runoff greater than the 10-year, 24-hour precipitation event to result from snowmelt or snowmelt coupled with a small precipitation event. 1.9 REFUSE PILE WATER QUALITY Water monitoring adjacent to the Lower Refuse Pile consists of the monitoring of alluvial wells around the refuse pile and periodic sampling of discharges from MB- 2R. Pond MB-2R treats surface water runoff from the refuse pile and adjacent disturbed areas and any discharge from the underdrain. Historic groundwater quality data from wells SG-1, GP-1, GP-3, GP-4, and GP-5 are incorporated into the data tables found in Appendix H. Quality parameters of Pond MB-2R discharge aze presen[ed in Table 2.4-1 and Table J-1, Appendix J. The sediment ponds are typically treated with cationic flocculent when necessary to speed clarification and settling of suspended solids. All ponds, MB-1, MB-2R, MB-3, MB-4 and MB-5 have manually controlled dewatering devices. Ponds MB-1, MB-2R and MB-5 are dewatered intermittently with the highest flows coming during early spring runoff. Pond MB-5 is responsive to a high spring groundwater table and sometimes has to be dewatered more often. Dewatering procedures take usually less than one day for all ponds except MB-5. R L:IO/IOA/OS/OS/95(B:OJam1 17 RE~15ED 10/02/96